The present invention relates generally to networking and, specifically, to a method and apparatus allowing a key manager node in a network to initiate a process of changing a group key for multiple members of a group in the network.
Internet Protocol (IP) multicasting is useful for disseminating data to a large group of receivers in a network. Multicasting of data is a form of network communication in which a transmitting node (a "sender") sends the data via a single message to multiple destinations at once. The multiple destinations are the recipients ("receivers") of the message. Other methods of network communication include broadcast, in which a sender transmits to all possible recipients, and unicast, in which the sender transmits only to one specific recipient. Multicast is described in more detail in T. A. Maufer, Deploying IP Multicast in the Enterprise, Prentice Hall PTR, 1998, which is herein incorporated by reference in its entirety to the extent that it does not conflict with the invention as described herein. A multicast sender may send a message to a selected group of receivers in a multicast group. A multicast group includes at least one sender that transmits data to nodes on a particular multicast address. A multicast group also includes one or more receivers. A receiver is a node that listens on a particular address in the network. Receivers become members of the group because they are interested in receiving messages. A node may be both a sender and a receiver of data to and from other nodes.
In certain conventional multicast systems, a sender distributes a group key to all nodes in the multicast group. Each member in the multicast group receives the same group key. This group key may be used by the one or more senders to encrypt data and by the receivers to decrypt the data sent to the group or to decrypt other, individual keys sent to the group members. When a member leaves a group or is no longer trusted, it is necessary to change the group key so that the former member will not be able to decrypt information encrypted with the group key. It is also wise for the sender to change the group key periodically in case the key has been compromised. It is also wise to change the group key if enough time has passed since the group key was last distributed that the group key could be compromised.
Some conventional multicasting systems, such as the "Enclave" system developed by Li Gong (as described in L. Gong, "Enclaves: Enabling Secure Collaboration over the Internet". IEEE Journal on Selected Areas in Communications, 15(3):567-575, April 1997) allow the sender to distribute a new key (encrypted separately for each member) directly via multicasting. Unfortunately, this method does not scale to large numbers of members, since the amount of data multicast to all members grows as the number of members grows.
As another example, the SKIP (Simple Key Management for Internet Protocols) protocol distributes keys that are deemed valid for a certain predetermined time period and updates these keys by a unicast. This distribution method causes a problem when a member leaves the group, since the member still has access to the group key until that group key expires. SKIP does not allow for quick key change when a member leaves the group or is suspected to be compromised.